Die-bonding method of led chip and led manufactured by the same

ABSTRACT

A die-bonding method is suitable for die-bonding a LED chip having a first metal thin-film layer to a substrate. The method includes forming a second metal thin film layer on a surface of the substrate; forming a die-bonding material layer on the second metal thin film layer; placing the LED chip on the die-bonding material layer with the first metal thin film layer contacting the die-bonding material layer; heating the die-bonding material layer at a liquid-solid reaction temperature for a pre-curing time, so as to form a first intermetallic layer and a second intermetallic layer; and heating the die-bonding material layer at a solid-solid reaction temperature for a curing time, so as to perform a solid-solid reaction. The liquid-solid reaction temperature and the solid-solid reaction temperature are both lower than 110° C., and a melting point of the first and second intermetallic layers after the solid-solid reaction is higher than 200° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No(s). 098140702 filed in Taiwan, R.O.C. on Nov.27, 2009, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a die-bonding method of a lightemitting diode (LED) chip and an LED, and more particularly to adie-bonding method capable of low-temperature die-bonding and obtaininghigh-temperature intermetallic layers as well as an LED having adie-bonded structure.

2. Related Art

The technology of adhering an LED chip to a lead frame has beendeveloped for many years. Die-bonding materials are approximatelydivided into two categories: one is high molecular conductive gluematerials, and the other is metal welding materials.

The first category can be seen in ROC Patent No. 463394 entitled“CHIP-TYPE LED AND MANUFACTURING METHOD THEREOF”. The method mainlyincludes: plating silver paste on a surface of a metal substrate,forming a plurality of lead frames after etching, die-bonding one end ofthe lead frame and connecting it to the opposite end by wire bonding,performing glue sealing and dicing so as to form a chip-type LED, inwhich lead frames exposed at the bottom form electrical contacts. Insuch practice, if glue is not spread uniformly in the bonding process,the die will not be fixed at the preset position, thereby influencingthe luminous efficiency. Next, in such die-bonding method, since thehigh molecular material has extremely low heat resistance, the silverpaste bonding layer is easily deteriorated in operation at a hightemperature. Further, since the high molecular material has low heatconductivity, the LED die cannot obtain a desirable heat dissipationeffect due to the low heat conductivity (the heat conductivitycoefficient of the silver paste is only 1 W/M-K). The life andphotoelectric conversion efficiency of the LED die are reduced as well.

The second category can be seen in ROC Patent Application PublicationNo. 200840079 entitled “DIE-BONDING MATERIAL AND METHOD OF LED PACKAGE”.The die-bonding method used in the patent application mainly adoptseutectic bonding based on the metal material of a substrate. First, alayer of eutectic bonding material in an appropriate range is coated onan upper surface of the metal substrate of the package structure. Then,an LED die is disposed on the eutectic bonding material of thesubstrate. The finished product passes through a hot plate, an oven, ora tunnel furnace to have an appropriate temperature, so as to accomplishthe eutectic bonding. This technology employs the eutectic bondingmaterial, and forms a bonding layer of a metal material, and thusachieves better heat dissipation and heat resistance than the silverpaste. A part of the eutectic bonding material employed in this patenttechnology has a high melting point, so that thermal stress easilyremains on the LED die in bonding, which damages the die. Although theother part of the eutectic bonding material is a low melting pointalloy, after bonding of such bonding material is completed, if the LEDis used in an environment of 70-80° C., the bonding layer will besoftened, and the contact reliability is greatly impaired.

In addition to the above technologies, US Patent Application PublicationNo. 2007/0141749 has disclosed introducing ultrasonic waves in thedie-bonding process and ionizing the bonding surface by the ultrasonicwaves, so as to lower the heating temperature and reduce the thermalstress. This method requires the addition of ultrasonic equipment, whichincreases the manufacturing cost. Meanwhile, if the ultrasonic waves areoperated improperly, the LED die may be vibrated directly to be cracked.

SUMMARY OF THE INVENTION

Accordingly, the present invention is a die-bonding method of an LEDchip and an LED applying the same. The die-bonding method of the presentinvention can accomplish die-bonding at a low temperature of 110° C.,and enable a bonded alloy after the die-bonding to have a melting pointhigher than 200° C., and thus can overcome the disadvantages andproblems of the above methods.

According to an embodiment, a die-bonding method of an LED chip issuitable for bonding the LED chip and a substrate. The LED chip has afirst metal thin film layer. The die-bonding method comprises: forming asecond metal thin film layer on a surface of the substrate; forming adie-bonding material layer on the second metal thin film layer, in whicha melting point of the die-bonding material is lower than 110° C.;placing the LED chip on the die-bonding material layer with the firstmetal thin film layer contacting the die-bonding material; heating thedie-bonding material layer at a liquid-solid reaction temperature for apre-curing time, so as to respectively form a first intermetallic layerand a second intermetallic layer between the first metal thin filmlayer, the die-bonding material layer, and the second metal thin filmlayer; and heating the die-bonding material layer at a solid-solidreaction temperature for a curing time, so as to perform a solid-solidreaction, in which a melting point of the first intermetallic layer andthe second intermetallic layer after the solid-solid reaction is higherthan 200° C.

According to an embodiment, the liquid-solid reaction temperature isequal to or higher than the melting point of the die-bonding material.The solid-solid reaction temperature is lower than the melting point ofthe die-bonding material. A material of the first metal thin film layerand a material of the second metal thin film layer may be Au, Ag, Cu, orNi. A material of the die-bonding material layer may be Bi—In, Bi—In—Zn,Bi—In—Sn, or Bi—In—Sn—Zn. Materials of the first intermetallic layer andthe second intermetallic layer may be selected from a group consistingof a Cu—In—Sn intermetallics, an Ni—In—Sn intermetallics, an Ni—Biintermetallics, an Au—In intermetallics, an Ag—In intermetallics, anAg—Sn intermetallics, and an Au—Bi intermetallics.

According to an embodiment, an LED comprises a substrate, a second metalthin film layer, a second intermetallic layer, a first intermetalliclayer, a first metal thin film layer, and an LED chip stacked insequence. A material of the first metal thin film layer and a materialof the second metal thin film layer may be Au, Ag, Cu, or Ni. Materialsof the intermetallic layers may be a Cu—In—Sn, Ni—In—Sn, Ni—Bi, Au—In,Ag—In, Ag—Sn, or Au—Bi intermetallics.

According to the embodiment of the die-bonding method, first, pre-curing(liquid-solid reaction) may be performed on the LED chip at atemperature lower than 110° C. for about 0.1 to 1 second. Afterwards, asolid-solid reaction of about 30 minutes to 3 hours is performed at atemperature lower than 80° C., so as to accomplish the procedure ofdie-bonding the LED chip and the substrate. Since all die-bondingprocedures are performed at low temperatures, no thermal stress isgenerated in the LED chip. Next, in the LED manufactured by thedie-bonding method, the bonding material between the LED chip and thesubstrate is a metal material, and thus better heat conduction and heatdissipation effects are achieved. Further, since the generatedintermetallic compound has a melting point temperature higher than 200°C., the bonded alloy will not be softened even if the LED operates inthe environment of 70 to 80° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below for illustration only, and thusare not limitative of the present invention, and wherein:

FIG. 1 is a schematic flow chart of a die-bonding method of an LED chipaccording to an embodiment of the present invention;

FIG. 2A is a schematic structural view of an LED chip in the die-bondingmethod according to an embodiment of the present invention;

FIG. 2B is a schematic structural view of a substrate in the die-bondingmethod according to an embodiment of the present invention;

FIG. 2C is a schematic structural view of the substrate on which StepS52 is performed in the die-bonding method according to an embodiment ofthe present invention;

FIG. 2D is a schematic structural view of Step S54 in the die-bondingmethod according to an embodiment of the present invention;

FIG. 2E is a schematic view of an LED structure in Step S56 in thedie-bonding method according to an embodiment of the present invention;

FIG. 2F is a schematic view of an LED structure in Step S58 in thedie-bonding method according to an embodiment of the present invention;

FIG. 2G is a schematic view of another LED structure in Step S58 in thedie-bonding method according to an embodiment of the present invention;and

FIG. 3 is the microstructure of die-bonding material layer and a firstmetal thin film layer in the die-bonding method according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic flow chart of a die-bonding method of an LED chipaccording to an embodiment of the present invention. FIG. 2A is aschematic structural view of an LED chip in the die-bonding methodaccording to an embodiment of the present invention. FIG. 2B is aschematic structural view of a substrate in the die-bonding methodaccording to an embodiment of the present invention.

Referring to FIGS. 1, 2A, and 2B, the die-bonding method of the LED chipis suitable for bonding the LED chip 10 and the substrate 20. The LEDchip 10 may be an LED having a p-i-n structure, for example, but notlimited to, GaN, GaInN, AlInGaP, AlInGaN, AlN, InN, GaInAsN, GaInPN, ora combination thereof.

The spectrum of light emitted by the LED chip 10 may be any visiblelight spectrum (380 nm to 760 nm) or other spectrums. The LED chip 10may be formed as a horizontal structure (Sapphire base), a verticalstructure (Thin-GaN LED), or a Flip-Chip.

The LED chip 10 has a first metal thin film layer 12. A material of thefirst metal thin film layer 12 may be Au, Ag, Cu, or Ni. The first metalthin film layer 12 may be plated on a surface of the LED chip 10 byelectroplating, sputtering, or evaporation. A thickness of the firstmetal thin film layer 12 may be, but not limited to, 0.2 μm to 2.0 μm.For example, the thickness is 0.5 μm to 1.0 μm.

In the LED chip 10 having the first metal thin film layer 12, the firstmetal thin film layer 12 is usually not directly plated on the dicedchip; instead, the first metal thin film layer 12 is plated on a backside of an LED wafer by electroplating or other methods, and then thewafer is diced and split.

The substrate 20 may be a lead frame, a printed circuit board (PCB), asubstrate having a plastic reflective cup, or a ceramic substrate. Amaterial of the substrate 20 may be a pure element such as Cu, Al, Fe,or Ni or an alloy added with a small amount of other elements. Thematerial of the substrate 20 may also be Si, AlN, or low-temperaturecofired ceramics (LTCC).

Reference is made to FIG. 1 as well as FIGS. 2B, 2C, 2D, 2E, and 2F forthe die-bonding method of the LED chip 10. As can be known from thefigures, the die-bonding method of the LED chip 10 comprises thefollowing steps.

In Step S50, a second metal thin film layer 22 is formed on a surface ofthe substrate 20 (as shown in FIG. 2B).

In Step S52, a die-bonding material layer 30 is formed on the secondmetal thin film layer 22, in which a melting point of the die-bondingmaterial layer 30 is lower than 100° C. (as shown in FIG. 2C).

In Step S54, the LED chip 10 is placed on the die-bonding material layer30 with the first metal thin film layer 12 contacting the die-bondingmaterial layer 30 (as shown in FIG. 2D).

In Step S56, the die-bonding material layer 30 is heated at aliquid-solid reaction temperature for a pre-curing time, so as torespectively form a first intermetallic layer 32 and a secondintermetallic layer 34 between the first metal thin film layer 12, thedie-bonding material layer 30, and the second metal thin film layer 22(as shown in FIG. 2E).

In Step S58, the die-bonding material layer 30 is heated at asolid-solid reaction temperature for a curing time, so as to perform asolid-solid reaction, in which a melting point of the firstintermetallic layer 32′ and the second intermetallic layer 34′ after thesolid-solid reaction is higher than 200° C. (as shown in FIG. 2F).

Reference is made to FIG. 2B for Step S50. The second metal thin filmlayer 22 may be formed on the substrate 20 by a process such aselectroplating, sputtering, or evaporation. A material of the secondmetal thin film layer 22 may be Au, Ag, Cu, or Ni. A thickness of thesecond metal thin film layer 22 may be, but not limited to, 0.2 μm to2.0 μm. For example, the thickness is 0.5 μm to 1.0 μm.

Referring to FIG. 2C, subsequent to Step S50, in Step S52, a die-bondingmaterial layer 30 may be formed on the second metal thin film layer 22by electroplating, evaporation, sputtering, or placing solder paste. Amaterial of the die-bonding material layer 30 may be Bi—In, Bi—In—Sn,Bi—In—Sn—Zn, or Bi—In—Zn. A melting point of Bi—In is about 110° C., amelting point of Bi-25In-18Sn is about 82° C., a melting point ofBi-20In-30Sn-3Zn is about 90° C., and a melting point of Bi-33In-0.5Znis about 110° C. A thickness of the die-bonding material layer 30 maybe, but is not limited to, 0.2 μm to 2.0 μm. For example, the thicknessis 0.5 μm to 1.0 μm.

Referring to FIG. 2D, in Step S54, the LED chip 10 is placed on thedie-bonding material layer 30 with the first metal thin film layer 12contacting the die-bonding material layer 30, as shown in FIG. 2D.

Then, Step S56 is performed in which the die-bonding material layer 30is heated at a liquid-solid reaction temperature for a pre-curing time,so as to respectively form a first intermetallic layer 32 and a secondintermetallic layer 34 between the first metal thin film layer 12, thedie-bonding material layer 30, and the second metal thin film layer 22(as shown in FIG. 2E). The liquid-solid reaction temperature may beequal to or higher than a melting temperature of the die-bondingmaterial layer 30. If the material of the die-bonding material layer 30is Bi—In—Sn, the liquid-solid reaction temperature may be 82° C. ormore. The heating manner may be laser heating, hot air heating, infraredheating, thermocompression bonding, or ultrasonic assistedthermocompression bonding.

The ambient temperature may be directly raised to the liquid-solidreaction temperature, or the die-bonding material layer 30 may bedirectly heated, or the substrate 20 may be directly heated and thenheat may transfer to the die-bonding material layer 30. Heating isperformed at, for example, but not limited to, the bottom of thesubstrate 20 directly by laser (i.e., heating is performed below thesubstrate 20 as shown in FIG. 2E).

The heating time (the pre-curing time) may be, but is not limited to,0.1 second to 2 seconds, for example, 0.2 second to 1 second. Theheating time may be appropriately adjusted depending on the condition ofthe liquid-solid reaction. The heating time may be the time taken forforming the first intermetallic layer 32 and the second intermetalliclayer 34 respectively between the first metal thin film layer 12, thedie-bonding material layer 30, and the second metal thin film layer 22.Step S56 can be construed as completed even if the formed firstintermetallic layer 32 and second intermetallic layer 34 are very thin.That is to say, as long as the first intermetallic layer 32 and thesecond intermetallic layer 34 are formed between the first metal thinfilm layer 12, the die-bonding material layer 30, and the second metalthin film layer 22, i.e., the bonding effect is produced, Step S56 canbe stopped to proceed to the next step (S58). Definitely, increasing thepre-curing time to form more first intermetallic layers 32 and secondintermetallic layers 34 in the process is also implementable.

The heating operation in Step S56 may also be referred to as apre-curing procedure, which aims to pre-fix the LED chip 10 and thesubstrate 20 according to the current alignment, so as to facilitate thesubsequent process. Since the temperature of the pre-curing proceduremay be equal to slightly higher than the melting point of thedie-bonding material layer 30, and the pre-curing time is quite short,the alignment can be effectively maintained without exerting anyinfluence such as a thermal stress on the LED chip 10.

Materials of the formed first intermetallic layer 32 and secondintermetallic layer 34 are related to the first metal thin film layer 12and the second metal thin film layer 22, which will be described indetail later.

Finally, Step S58 is performed in which the die-bonding material layer30 is heated at a solid-solid reaction temperature for a curing time, soas to perform a solid-solid reaction. The solid-solid reactiontemperature may be lower than the melting point of the die-bondingmaterial layer 30, and may be, but not limited to, 40 to 80° C. Thecuring time may be adjusted according to the solid-solid reactiontemperature. For example, when the solid-solid reaction temperature ishigh, the curing time may be short. When the solid-solid reactiontemperature is low, the curing time may be long. The curing time may be30 minutes to 3 hours.

The solid-solid reaction aims to diffuse alloy elements of thedie-bonding material layer 30 and elements of the first metal thin filmlayer 12 and the second metal thin film layer 22. The time of thesolid-solid reaction may be determined as the time required fordiffusing most of alloy elements in the die-bonding material layer 30.

Step S58 may be performed by batch operation in the actual application.That is to say, multiple semi-finished products obtained after Step S56are gathered, and Step S58 is performed by hot air heating, ovenheating, infrared heating, or hot plate heating unitedly.

Since the solid-solid reaction temperature in Step S58 is lower than themelting point of the die-bonding material layer 30, the alignmentachieved in Step S56 is not influenced.

The LED formed after Step S58 has several possible structures. The firststructure of the LED can be seen in FIG. 2F. As can be known from thefigure, the LED comprises the substrate 20, the second metal thin filmlayer 22, the second intermetallic layer 34′, the first intermetalliclayer 32′, the first metal thin film layer 12, and the LED chip 10stacked in sequence. Materials of the first metal thin film layer 12 andthe second metal thin film layer 22 are selected from a group consistingof Au, Ag, Cu, and Ni. Materials of the two intermetallic layers 32′ and34′ comprise a Cu—In—Sn intermetallics (having a melting point above atleast 400° C.), an Ni—In—Sn intermetallics (having a melting point aboveabout 700° C.), an Ni—Bi intermetallics (having a melting point above atleast 400° C.), an Au—In intermetallics (having a melting point above atleast 400° C.), an Ag—In intermetallics (having a melting point above atleast 250° C.), an Ag—Sn intermetallics (a melting point above at least450° C.), and an Au—Bi intermetallics (having a melting point above atleast 350° C.).

Next, it should be noted that, the materials of the first intermetalliclayer 32 and the second intermetallic layer 34 formed in the pre-curingprocedure (i.e., shown in FIG. 2E) may be different from those of thefirst intermetallic layer 32′ and the second intermetallic layer 34′after the solid-solid reaction. In the pre-curing procedure, althoughthe liquid-solid reaction temperature reaches the melting point of thedie-bonding material layer 30, since Step S56 can be stopped immediatelyafter the first intermetallic layer 32 and the second intermetalliclayer 34 are formed, a part of alloy elements in the die-bondingmaterial layer 30 are not diffused. For example, if the die-bondingmaterial layer 30 contains In, In is easily diffused first to form anintermetallic layer during the liquid-solid reaction.

Three examples are listed below to show the materials of the secondmetal thin film layer 22, the second intermetallic layer 34′, the firstintermetallic layer 32′, and the first metal thin film layer 12 of theLED shown in FIG. 2E in Steps S54, S56, and S58 in the pre-curingprocedure.

Layer Step S54 Step S56 Step S58 [First Embodiment of LED Structure inFIG. 2E] First metal thin film layer Ag Ag Ag First intermetallic layerNo Au—In, Ag—In, Au—In, Ag—In, Ag—Sn, Au—Bi, or Ag—Sn, Au—Bi, or otherintermetallics, other intermetallics, for example, Ag₂In for example,Ag₂In Die-bonding material layer Bi—In—Sn Bi—In—Sn No Secondintermetallic layer No Au—In, Ag—In, Au—In, Ag—In, Ag—Sn, Au—Bi, orAg—Sn, Au—Bi, or other intermetallics, other intermetallics, forexample, AuIn₂ for example, Au2Bi + AuIn₂ Second metal thin film layerAu Au Au [Second Embodiment of LED Structure in FIG. 2E] First metalthin film layer Ni Ni Ni First intermetallic layer No Ni—In—Sn, Ni—Bi,or Ni—In—Sn, Ni—Bi, or other intermetallics other intermetallicsDie-bonding material layer Bi—In—Sn Bi—In—Sn No Second intermetalliclayer No Ni—In—Sn, Ni—Bi, or Ni—In—Sn, Ni—Bi, or other intermetallicsother intermetallics Second metal thin film layer Ni Ni Ni [ThirdEmbodiment of LED Structure in FIG. 2E] First metal thin film layer CuCu Cu First intermetallic layer No Cu—In—Sn Cu—In—Sn intermetallicsintermetallics Die-bonding material layer Bi—In—Sn Bi—In—Sn No Secondintermetallic layer No Cu—In—Sn Cu—In—Sn intermetallics intermetallicsSecond metal thin film layer Cu Cu Cu

Melting points of the first intermetallic layer 32′ and the secondintermetallic layer 34′ in the first embodiment of the LED structure inFIG. 2E are both higher than 200° C. Even if the LED is operated at atemperature above 80° C. for a long time in the future, the bondingmedium will not be softened, so that the alignment in the process can bemaintained continuously to obtain a high luminous efficiency.

Another structure of the LED formed after Step S58 can be seen in FIG.2G. As can be known from the figure, the LED comprises the substrate 20,the second metal thin film layer 22, the second intermetallic layer 34′,an intermediate layer 36, the first intermetallic layer 32′, the firstmetal thin film layer 12, and the LED chip 10 stacked in sequence. Amaterial of the intermediate layer 36 is related to materials of thedie-bonding material layer 30, the second intermetallic layer 34′, andthe first intermetallic layer 32′. If the material of the die-bondingmaterial layer 30 is Bi—In—Sn, the material of the intermediate layer 36is possibly Sn. That is, only Sn remains in the die-bonding materiallayer 30 after the solid-solid reaction.

Since a melting point of Sn is about 230° C. which is also higher than200° C., the above purpose of not softening the LED in use can beachieved. That is to say, the die-bonding material layer 30 maydisappear by reaction after the solid-solid reaction or remain to formthe intermediate layer 36.

The bonding state of Bi—In—Sn and Ag can be seen in FIG. 3. FIG. 3 is amicrostructure of the die-bonding material layer 30 and the first metalthin film layer 12 in the die-bonding method according to an embodimentof the present invention. In this experiment, a Bi—In—Sn alloy ofBi-25In-18Sn is disposed on a silver plate, a temperature of 85° C. isapplied for a period of time, and then alloy analysis is performed toobtain the microstructure. As can be seen from the figure, an Ag₂Inbonding layer is formed between the Bi—In—Sn and the Ag plate. Thereby,it can be known that, the die-bonding material layer 30 used in thepresent invention can form a bonding layer with silver at a lowtemperature.

It can be known from the embodiments of the die-bonding method and theLED structure after die-bonding that, the LED chip 10 can be pre-curedon the substrate 20 using a low temperature and a short time in thedie-bonding process without the problem of misalignment. Afterwards, asolid-solid reaction is performed at a lower temperature. The firstintermetallic layer 32′ and the second intermetallic layer 34′ after thereaction have high melting points (higher than 200° C.). Therefore, evenif the LED after die-bonding is operated at a temperature higher than80° C. for a long time, the first intermetallic layer 32′ and the secondintermetallic layer 34′ will not be softened, and the alignmentprecision is not influenced. Further, since the temperatures used in theprocess are all far lower than 100° C., the problem that a thermalstress remains or is concentrated on the LED chip 10 and othercomponents (such as the substrate 20 and the plastic reflective cup)will not occur in the die-bonding process. An LED having highreliability is obtained. Finally, since the pre-curing procedure can beperformed by laser heating, the pre-curing time is shortened a lot.Moreover, since batch operation can be employed in the solid-solidreaction, the present die-bonding method can obtain a much higherthroughput than the conventional art.

1. A die-bonding method of a light emitting diode (LED), suitable forbonding the LED chip and a substrate, wherein the LED chip has a firstmetal thin film layer, the die-bonding method comprising: forming asecond metal thin film layer on a surface of the substrate; forming adie-bonding material layer on the second metal thin film layer, whereina melting point of the die-bonding material is lower than 110° C.;placing the LED chip on the die-bonding material layer with the firstmetal thin film layer contacting the die-bonding material; heating thedie-bonding material layer at a liquid-solid reaction temperature for apre-curing time, so as to respectively form a first intermetallic layerand a second intermetallic layer between the first metal thin filmlayer, the die-bonding material layer, and the second metal thin filmlayer; and heating the die-bonding material layer at a solid-solidreaction temperature for a curing time so as to perform a solid-solidreaction, wherein a melting point of the first intermetallic layer andthe second intermetallic layer after the solid-solid reaction is higherthan 200° C.
 2. The die-bonding method according to claim 1, wherein theliquid-solid reaction temperature is equal to or higher than the meltingpoint of the die-bonding material layer.
 3. The die-bonding methodaccording to claim 1, wherein the solid-solid reaction temperature islower than the melting point of the die-bonding material layer.
 4. Thedie-bonding method according to claim 1, wherein the step of heating thedie-bonding material layer at the solid-solid reaction temperature so asto perform the solid-solid reaction is: heating the die-bonding materiallayer at the solid-solid reaction temperature so as to perform thesolid-solid reaction, until the solid-solid reaction between thedie-bonding material, the first metal thin film layer, and the secondmetal thin film layer is completed.
 5. The die-bonding method accordingto claim 1, wherein a material of the first metal thin film layer isselected from a group consisting of Au, Ag, Cu, and Ni, and a materialof the second metal thin film layer is selected from a group consistingof Au, Ag, Cu, and Ni.
 6. The die-bonding method according to claim 5,wherein a material of the die-bonding material layer is selected from agroup consisting of Bi—In, Bi—In—Zn, Bi—In—Sn, and Bi—In—Sn—Zn.
 7. Thedie-bonding method according to claim 6, wherein the liquid-solidreaction temperature is 85° C., and the pre-curing time is 0.1 second to1 second.
 8. The die-bonding method according to claim 6, wherein thesolid-solid reaction temperature is 40° C. to 80° C., and the curingtime is 30 minutes to 3 hours.
 9. The die-bonding method according toclaim 6, wherein materials of the first intermetallic layer and thesecond intermetallic layer are selected from a group consisting of aCu—In—Sn intermetallics, an Ni—In—Sn intermetallics, an Ni—Biintermetallics, an Au—In intermetallics, an Ag—In intermetallics, anAg—Sn intermetallics, and an Au—Bi intermetallics.
 10. A light emittingdiode (LED), comprising: a substrate; a second metal thin film layer,located on the substrate, wherein a material of the second metal thinfilm layer is selected from a group consisting of Au, Ag, Cu, and Ni; asecond intermetallic layer, located on the second metal thin film layer:a first intermetallic layer, located on the second intermetallic layer;a first metal thin film layer, located on the first intermetallic layer,wherein a material of the first metal thin film layer is selected from agroup consisting of Au, Ag, Cu, and Ni, materials of the first andsecond intermetallic layers are selected from a group consisting of aCu—In—Sn intermetallics, an Ni—In—Sn intermetallics, an Ni—Biintermetallics, an Au—In intermetallics, an Ag—In intermetallics, anAg—Sn intermetallics, and an Au—Bi intermetallics; and an LED chip,located on the first metal thin film layer.
 11. The LED according toclaim 10, further comprising an intermediate layer sandwiched betweenthe first intermetallic layer and the second intermetallic layer,wherein a material of the intermediate layer is selected from a groupconsisting of Sn, Bi, In, and Zn.